Generator for a generic authorizer expects a server to be specified

When running this:

```bash
php artisan jsonapi:authorizer organiser
```

You get the error message: 

```
You must use the server option when you have more than one API.
```

However this is generating a generic authorizer, which goes in the `App\JsonApi\Authorizers` namespace - i.e. does not relate to a specific server. In this scenario it should not need the server to be specified.